1 Contract Driven Development = Test Driven Development - Writing Test - Cases

Although unit tests are recognized as an important tool in software development, programmers prefer to write code, rather than unit tests. Despite the emergence of tools like JUnit which automate part of the process, unit testing remains a time-consuming, resource-intensive, and not particularly appealing activity. This paper introduces a new method, called ContractDriven Development, that takes the task of writing unit tests o the developers' shoulders, while still taking advantage of the developers' knowledge of the intended semantics and structure of the code. This methodology exploits actions that programmers perform anyway as part of the normal process of writing code, by extracting test cases from failureproducing runs of the system that the programmers trigger. The approach is based on the presence of contracts in code, which act as the oracle of the test cases. The test cases are extracted completely automatically, run in the background when the code evolves, and can easily be maintained over versions. The tool implementing this methodology is called Cdd and is available both in binary and in source form.